Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$169.79	5.741%	$179.5376	$179.54	$179.55	$179.50
Purchase #2	$134.93	3.873%	$140.1558	$140.16	$140.15	$140.20
Purchase #3	$183.75	4.353%	$191.7486	$191.75	$191.75	$191.70
Purchase #4	$42.34	7.179%	$45.3796	$45.38	$45.40	$45.40
Purchase #5	$31.86	6.623%	$33.9701	$33.97	$33.95	$34.00
Purchase #6	$207.33	10.110%	$228.2911	$228.29	$228.30	$228.30
Purchase #7	$177.68	3.777%	$184.391	$184.39	$184.40	$184.40
7 purchase totals =	$947.68		$1,003.4738	$1,003.48	$1,003.50	$1,003.50